On Sun, 25 Jan 2026 00:52:12 -0500, guoren@kernel.org wrote:

> Unlike no4lvl, no5lvl still continues detect satp, which
> requires va=pa mapping. When pa=0x800000000000, no5lvl
> would fail in Sv48 mode due to an illegal VA value of
> 0x800000000000.
> 
> So, prevent detecting the satp flow for no5lvl, when
> vaddr is invalid. Add the is_vaddr_valid() function for
> checking.
> 
> Fixes: 26e7aacb83df ("riscv: Allow to downgrade paging mode from the command line")
> Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
> Cc: Björn Töpel <bjorn@rivosinc.com>
> Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
> ---
> Changelog:
> 
> v2:
>  - Use is_vaddr_valid() instead of simple return.
>  - Don't change the original no5lvl code logic.
> 
> v1:
> https://lore.kernel.org/linux-riscv/20260118145441.291302-1-guoren@kernel.org/
> ---
>  arch/riscv/mm/init.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index addb8a9305be..bfea9f73e703 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -852,6 +852,27 @@ static void __init set_mmap_rnd_bits_max(void)
>  	mmap_rnd_bits_max = MMAP_VA_BITS - PAGE_SHIFT - 3;
>  }
>  
> +static bool __init is_vaddr_valid(unsigned long va)
> +{
> +	unsigned long up = 0;
> +
> +	switch (satp_mode) {
> +	case SATP_MODE_39:
> +		up = 1UL << 38;
> +		break;
> +	case SATP_MODE_48:
> +		up = 1UL << 47;
> +		break;
> +	case SATP_MODE_57:
> +		up = 1UL << 56;
> +		break;
> +	default:
> +		return false;
> +	}
> +
> +	return (va < up) || (va >= (ULONG_MAX - up + 1));
> +}
> +
>  /*
>   * There is a simple way to determine if 4-level is supported by the
>   * underlying hardware: establish 1:1 mapping in 4-level page table mode
> @@ -893,6 +914,9 @@ static __init void set_satp_mode(uintptr_t dtb_pa)
>  			   set_satp_mode_pmd + PMD_SIZE,
>  			   PMD_SIZE, PAGE_KERNEL_EXEC);
>  retry:
> +	if (!is_vaddr_valid(set_satp_mode_pmd))
> +		goto out;
> +
>  	create_pgd_mapping(early_pg_dir,
>  			   set_satp_mode_pmd,
>  			   pgtable_l5_enabled ?
> @@ -915,6 +939,7 @@ static __init void set_satp_mode(uintptr_t dtb_pa)
>  		disable_pgtable_l4();
>  	}
>  
> +out:
>  	memset(early_pg_dir, 0, PAGE_SIZE);
>  	memset(early_p4d, 0, PAGE_SIZE);
>  	memset(early_pud, 0, PAGE_SIZE);

Tested-by: Chen Pei <cp0613@linux.alibaba.com>

Thanks,
Pei